Devices used to trace and detect audio signals in metallic conductors are commonly referred to as tone probes, audio tone probes, inductive amplifiers, etc. These devices are used by telecommunication, LAN, WAN or cable technicians to identify, trace and locate a particular conductor. In particular these devices are used to identify opposite ends of a conductor wherein only the ends of the conductor are visible or accessible. An audio tone probe is used in conjunction with a tone generator. Specifically, the tone generator is used to send a tracing tone signal over a conductor at a first location, the signal having either a single frequency or having multiple frequencies. The tracing tone signal is carried by the conductor to be traced to a second location where the conductor is to be identified using the audio tone probe. The conductor to be identified may, for example, be in a cable and therefore maybe present along with many other nearby metal conductors or wires. Often other wires and conductors are carrying other signals, such as for example, electrical AC or DC control signals, etc. Occasionally faults may occur that cause unexpected voltages to be present on the conductor to be traced, for example, non-telecommunication signals or even AC mains power may be present on the conductor to be traced. These signals may be hazardous to the technician. Thus, the need for detection of hazardous voltages on the conductors arises in order to warn the technician of these hazardous voltages while they are tracing or identifying the desired metal conductors.
Conventional tone probes used to identify the conductor carrying the tracing tone signal may be either of the unfiltered type or the filtered type. Alternatively, a conventional tone probe may include both unfiltered or filtered modes, allowing the user to select either a filtered mode or an unfiltered mode of operation.
An unfiltered tone probe receives electrical signals in a particular frequency range and converts all of the received electrical signals to an audio signal. The received signals may include for example, the applied tone signal, noise, mains, etc. When working with communications cabling such as that for a telephone system, there is often a risk that a cable carrying mains has accidentally come in contact with the communications cabling. With an unfiltered probe, the probe will receive the tracing tone signal, noise, and a “mains hum” or buzzing sound which results from the mains signal. This mains hum may also be present in many locations which are near electrical equipment. A skilled technician may be able to differentiate between the conductor carrying the tracing tone signal from the conductor carrying hazardous electrical voltages by listening to the mains hum while tracing the conductors. Thus, the mains hum can be utilized by the technician as an indication that the conductor may be carrying potentially hazardous voltages. If the noise level (e.g. electrical buzz from ambient noise from nearby conductors) is greater than the tracing tone signal level, it becomes difficult for the technician to trace or locate the desired conductor (i.e. the conductor to which the tracing tone signal is applied).
Filter audio tone probes utilize filtration techniques to make the signal of interest, e.g. the tracing tone signal, more distinctive and therefore easier to differentiate from the noise or unwanted electrical signals. Examples of filtered audio tone probes include the instruments sold by Greenlee Textron, Inc. under the names 500J and 200 XP. U.S. Pat. No. 5,557,099 to Clement and Clark, for example, discloses a tone probe which utilizes selective filtering technology.
Filtration suppresses the ambient or noise induced as a result of nearby electrical conductors or hazardous conductors through band pass filtration or comb filtration techniques or a combination of these techniques. Using these filtration techniques, the noise and “mains hum” is removed from the audio path making it easier to detect the tracing signal tone and thereby identify the desired conductor. Filtering the mains hum, however, increases the probability that the unskilled technician will come in contact with hazardous conductors while tracing the conductors. Because the mains hum which is induced in the conductor is filtered from the audio tone received by the technician, the technician does not receive warning of the presence of hazardous voltages on the conductor. Thus, if a technician intends to use a filtered tone probe for tracing a conductor, the technician should in order to avoid hazardous conditions, also use a mains-rated multimeter. Use of a mains-rated multimeter or non-contact AC voltage detector will inform the technician as to whether hazardous AC mains voltages are present before using communications test equipment, such as for example, a filtered tone probe. Examples of non-contact AC voltage detectors include Greenlee's GT-11 and GT-12 devices.
One problem with using a mains-rated multimeter or non-contact voltage detector for testing for hazardous voltages prior to utilizing communications test equipment is that the technician is required to obtain and carry additional equipment. In addition, the technician is required to perform a preliminary step (i.e. test for mains) prior to tracing the conductor.
Pair tracing probe manufacturers have attempted to avoid mains and other noise signals by using alternative signal processing techniques. One alternative techniques involves the generation of special signals which are not reproduced directly but rather are reproduced by creating a representation of the generated signal. This technique is not intuitive and the response time of the detection algorithms is slow which leads to confusing results.
Accordingly, a need exists for an apparatus and method for tracing tones on a conductor while at the same time providing the user with a warning of hazardous voltages on the conductor. Additionally, a need exists for providing the user with assurances with respect to the integrity of the apparatus.